The present invention relates to noncorrecting lens blanks, which make it possible to obtain noncorrecting lenses by trimming, and the shape and dimensions of which are matched for mounting in or on a suitable frame of a pair of glasses.
The invention also relates to pairs of glasses, intended for solar or industrial protection, comprising two noncorrecting lenses, each one capable of being obtained by trimming a blank as defined above, these lenses being mounted or supported in or by a suitable frame.
More specifically, the invention relates to noncorrecting lens blanks which are polarizing or which have another optical function and to glasses obtained from such blanks, and consequently, comprising two noncorrecting lenses which are also polarizing or which have this other function. The latter is, for example, the photochromic function which alters the intensity of the color of the glass according to the intensity of the light received. It is possible also to envision having an infrared filter, or any other function.
At present, in order to obtain a polarizing noncorrecting lens blank, the starting material used is a composite sheet comprising a filtering film made of a polarizing material, inserted between two layers of a light-transmitting transparent material, preferably made of a thermoplastic, for example a polycarbonate. Next, a strip delimited by a peripheral border is flat cut in this composite sheet. Then this strip is thermoformed in order to obtain a blank, according to any predetermined radius of curvature, and delimited between one outer convex face and an opposite inner and concave face. On the basis of the preferred plane of polarization of the filtering film, and given the angular orientation of said film with respect to the two layers of the transparent material, the blank acquires a preferred plane of polarization. The latter preferably remains substantially parallel to the optical axis of the lens which will then be obtained by trimming said blank.
The blanks and lenses obtained from composite thermoformed sheets have mediocre, even inadequate, optical characteristics, in particular for large curvatures (base 6 and above). This is because the power and prism values of the lens obtained by trimming such a blank do not comply with current standards. This results especially from the fact that the thermoforming operation does not allow control of the relative position of the anterior and posterior diopters, and therefore the position of the optical center of the blank.
Moreover, document FR 2 740 231 describes and proposes a noncorrecting lens blank having good optical properties, in particular power and prism properties, including for glasses of strong curvature corresponding to a mean radius of curvature at the most equal to about 90 mm. This blank comprises a transparent strip having, on the one hand, a geometric axis passing through said strip and defining a geometric center, and, on the other hand, an optical axis defining an optical center. In addition, the strip, seen in elevation, has a generally noncircular perimeter, and the optical axis and the geometric axis and consequently the optical and geometric centers, are distinct and offset at an angle and by a predetermined distance one from the other.
The subject of the present invention is a noncorrecting lens blank integrating any optical function such as, for example, polarization, making it possible to obtain substantially the same optical characteristics as those obtained according to document FR 2 740 231, notwithstanding the presence of a film in the blank allowing the latter to integrate a function such as polarization, infrared filtration or any other known function that can be applied to a lens.
According to the present invention, the blank comprises a composite strip, delimited by a peripheral border and between an outer convex face and an opposite inner concave face, said composite strip consisting of at least one transparent material, transmitting light from the outer face to the inner face, and said composite strip incorporating a film integrating the optical function. This composite strip has, in a first embodiment according to the invention, the following structure and arrangement:
firstly, the strip comprises a matrix of transparent material determining the inner face of the lens from the inner side; and in this matrix from the outer side, a convex housing is reserved, whose flat surface occupies the majority of the surface of the composite strip; and
a piece of film, matched in shape and in dimensions to the convex housing, occupies the latter.
This composite strip has, in a second embodiment according to the invention, the following structure and arrangement:
firstly, the strip comprises a matrix of transparent material, determining the outer face of the lens from the outer side; and in this matrix, from the inner side, is reserved a concave housing whose flat surface occupies the majority of the surface of the composite strip; and
a piece of film, matched in shape and in dimensions to the concave housing, occupies the latter.
A blank obtained according to the invention makes it possible to control, especially in terms of tolerance and positioning, the proper orientation of this blank during its trimming, and consequently the quality of the lens thus obtained.
The housing is, for example, a convex housing placed on the outer face of the matrix. By virtue of the arrangement of the film on the outer side of the blank, the outer face of the film corresponds mainly to the outer convex face of the blank, or subsequently of the lens. In addition, the stresses generated in the injected transparent material, which usually generate an unwanted polarization, are virtually imperceptible to the eye of the user of the glasses.
Advantageously, the piece of film has a constant thickness.
By way of first example, the peripheral border comprises two truncated concentric circular edges, separated by two straight parallel edges, for example of identical length, and the perimeter of the housing has substantially the same profile as that of the peripheral border, and is fitted in a homothetic manner in the latter.
By way of second example, the peripheral border is at least predominantly circular, and the perimeter of the housing comprises two truncated concentric circular edges, separated by two parallel straight edges, for example of identical length. In this example, the peripheral border comprises, for example, a predominant circular part and a straight part, which is coincident with a straight edge of the housing.
In one embodiment, the inner and outer faces each have, at least in part, a symmetry of revolution about the same axis, called the optical axis, determining, if required, an optical center on the two outer and inner faces of the composite strip. In this case, the peripheral border has, for example, at least in part, a profile of revolution about a geometric center, placed at a distance and distinct from the optical axis.
The outer face of the composite strip is advantageously coated by at least one layer of a material chosen from the group comprising scratch-resistant materials, filtering materials and colored materials.
The film integrating the optical function may be a filtering film of a polarizing material and the angular orientation of the piece of filtering film in and with respect to the matrix of transparent material, about a normal axis passing through them, is then preferably chosen in order to give the blank a preferred plane of polarization, substantially parallel to a transverse plane intersecting it.
According to the invention, the preferred plane of polarization of the lense is chosen in order to exhibit any predetermined angular orientation (substantially perpendicular, parallel or other), with reference to an indicator or indicators usually present on the blank, in particular taking account of the interface existing between polarizing and transparent materials, or with reference to an indicator or indicators recorded on the blank, for example hollow or relief marks, making it possible to define one or more reference axes at the time of trimming.
By xe2x80x9csubstantially parallel or perpendicularxe2x80x9d, the way in which the curvature of the blank, and subsequently of the lens, considered in a vertical or horizontal insertion plane (with respect to the lens in position on the user""s head, via glasses) deviates the orientation of the plane of polarization, going from the edge toward the center of the blank or of the lens, is taken into consideration.
A blank with a piece of polarizing filtering film, obtained according to the invention, makes it possible to control the angular positioning of the preferred plane of polarization of the blank, especially in terms of tolerance, and then the lens obtained by trimming this blank.
For the first example above, that is to say when the peripheral border comprises two truncated concentric circular edges, separated by two straight parallel edges, for example of identical length, and when the perimeter of the convex housing has substantially the same profile as that of the peripheral border, and is fitted in a homothetic manner in the latter and when the piece of film is a piece of polarizing filtering film, then the piece of filtering film is advantageously cut in the polarizing film, so that the preferred plane of polarization is substantially parallel or perpendicular to each straight parallel edge of said piece, in view of which each straight parallel edge of the blank is substantially parallel or perpendicular to the preferred plane of polarization of the latter.
For the second example above, that is to say when the peripheral border is at least for the most part circular, and the perimeter of the convex housing comprises two truncated concentric circular edges separated by two straight parallel edges, for example of identical length, and when the piece of film is a piece of polarizing filtering film, then the piece of filtering film is advantageously cut in band shape in the polarizing film, such that the preferred plane of polarization is substantially parallel or perpendicular to each straight parallel edge of said piece, in view of which at least one straight line of separation between the matrix of the transparent material and the piece of filtering material is substantially parallel or perpendicular to the preferred plane of polarization of the blank.
These arrangements allow an immediate visualization of the plane of polarization of the blank, which allows the glasses manufacturers to trim said blank in order to keep the plane of polarization of the lens substantially parallel or perpendicular to the visual axis of the glasses in position on the user""s head.
When each of the inner and outer faces have, at least in part, a symmetry of revolution about the same axis, called the optical axis, determining an optical center on the outer and inner faces of the composite strip, if required, the optical axis is, for example, substantially parallel or perpendicular to the preferred plane of polarization of said blank for polarizing lenses. The geometric shape of the outer face and/or of the inner face of the composite strip, can also be determined such that in a plane of section substantially parallel or perpendicular to the preferred plane of polarization, the thickness of the composite strip decreases continually when moving away from the optical axis toward the outside. In the latter case, the geometric shape of the outer face and the geometric shape of the inner face correspond, for example, respectively to two spheres with centers spaced out along the optical axis.
When the peripheral border has, for example, at least in part, a profile of revolution about a geometric centre, placed at a distance and distinct from the optical axis, the optical axis and the geometric center advantageously determine a plane substantially parallel or perpendicular to the preferred plane of polarization of said blank for polarizing lenses.
The invention also relates to a pair of glasses comprising a frame and two noncorrecting lenses integrating an optical function such as, for example, polarization, supported by said frame, each lens comprising a composite strip delimited between an outer convex face and an opposite inner concave face, said composite strip consisting of at least one transparent material transmitting light from the outer face to the inner face, and said composite strip incorporating a film integrating the optical function. According to the invention, each lens comprises, from the inside toward the outside or conversely, a first thickness of transparent material, determining from the inner, outer side, respectively, said inner, outer face, respectively, and directly in contact with the first thickness, a second thickness of film, determining from the outer, inner side, respectively, said outer, inner face, respectively, of the lens.
When each lens of the pair of glasses is a polarizing lens, each lens is, for example, oriented at an angle with respect to the frame, about a normal axis passing through it, such that its preferred plane of polarization is substantially parallel or perpendicular to the horizontal plane of the pair of glasses, passing through the visual axis of the glasses in position on the user""s head.
The transparent material of a blank according to the invention can be obtained, for example by injection molding. The invention thus also relates to a mold for injecting the transparent material, consisting of a thermoplastic or thermosetting synthetic material, in order to obtain a blank as described above, said mold comprising two complementary parts which can be moved one with respect to the other, and which, once assembled one on the other, determine a gap whose volume and shape determine those of the strip; the part of the mold determining the outer face of the strip comprises means for positioning the convex piece of the film. Such a mold will especially be used for polarizing blanks.
A blank according to the invention can also be obtained by a production process comprising a step of overmolding the piece of film by extrusion. In this case, the pieces obtained after extrusion can be cut and thermoformed.
Another process of production means that the matrix of transparent material and the piece integrating the function are produced separately and in [sic] that these two components are subsequently adhesively bonded.
All these solutions make it possible to obtain a good optical quality, complying with the Gullstrand law.